Electrodepositing composition and process



Patented Feb. 15, 1949 UNITED STATES ELECTRODEPOSITING COMPOSITION AND PROCESS Allen G. Gray, Rocky River, Ohio, and William Franklin Gresham and Donald John Loder, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 7, 1943, Serial No. 493,756

13 Claims.

This invention relates to the electrodeposition of tin and is more particularly directed to tinplating compositions, tin-plating baths, and to processes for the electrodeposition of tin in the presence of a polydioxolane.

Tin-plating baths known to the art are subject to disadvantages which severely limit their usefulness. Organic addition agents have been em-, ployed in attempts to improve the character ofi, deposit obtained from such baths and while the 5 addition agents effect some refinement of crystal, structure and some modification in appearance the tin electrodeposits are of limited usefulness and the baths from which they are made are difficult and uneconomical to employ.

Tin electrodeposits produced from prior art baths are usually crystalline at even rather low current densities and at higher current-densities the deposits are spongy. They are not adherent and many are so poorly adherent that they can easily be removed from the base metal by rubbing. Deposits thus produced with prior art baths are not readily amenable to brightening by heat fusion. These and numerous other difiiculties have hampered commercial development of tin electroplating processes.

It is an object of this invention to provide compositions, baths, and processes by the use of which there may be obtained tin deposits which are dense, adherent, and of good appearance. It is a further object to provide tin-plating baths, compositions, and processes by means of which there may be obtained deposits that can be readily b ightened by fusion to a brilliant appearance and that can be subjected to lacquer baking operations without becoming discolored. Further objects of this invention will become apparent hereinafter.

The foregoing and other objects of this invention are attained by the use in a tin electrodepositing bath of a bath-soluble polydigxolane. By employing a polydioxolane in tin electroclepositing baths one obtains deposits of a markedly improved character.

Polydioxolanes may be used according to the present invention in any tin-plating bath. For purposes of illustration the following typical baths are given:

BATH I Grams per liter Stannous sulfate 54 Sulfuric acid (computed as H2SO4) 100 BATH II Grams per liter Stannous sulfate 100 Sulfuric acid (computed as H2SO4) 30 Tartaric acid 30 BATH 111 Grams per liter Stannous oxalate 50 Ammonium oxalate Oxalic acid 15 BATH IV The following alkaline bath is of the type shown in the Oplinger Patent 1,841,978 and in the Wernlund et a1. Patent 1,919,000.

Grams per liter Sodium stannate 120.0

Sodium hydroxide 7.5 Sodium acetate 15.0 Hydrogen peroxide 0.5

BATH V The following bath is not very stable when used over long periods of time but it is given because it is frequently mentioned in the literature and it is markedly benefited by the use of polyethers according to the present invention.

Grams per liter Stannous chloride 30 Sodium hydroxide BATH VI A bath of U. S. Patent 1,202,149 was made up as follows:

Grams per liter Stannous chloride dissolved in 10% phosphoric A bath was made up as in the Schliitter Patent 2,271,209 as follows:

- Grams per liter Stannous sulfate 45 Sulfuric acid (66 B.) 75

It will generally be found desirable to employ polydioxolanes according to the present invention in acid baths of the prior art though as will be pointed out more particularly hereinafter excellent results are obtained in alkaline baths and especially with baths such as bath IV given above.

Instead of using either the strongly acidic or basic tin solutions common in the art it will often be found most advantageous to use polydioxolanes according to the present invention in recently developed neutral solutions. These baths are only slightly acidic, having a pH above 1, and they have high conductivity and effective anode corrosion. These compositions are known as halogen-tin plating baths and the preferred baths are composed of an alkali fluoride-stannous chloride solution. These baths are described and claimed in Schweikher application, Serial No. 493,757, filed July 7, 1943, now Patent No. 2,407,579, Sept. 10, 1946.

In using halogen-tin baths the ratio of fluoride to stannous chloride must be carefully selected and related to the operating pH of the bath as more specifically described below. The baths may be made up with stannous chloride and with an alkali fluoride, say sodium, potassium, or ammonium fluoride. When reference is made hereinafter to an alkali fluoride it will be understood that sodium, potassium, or ammonium fluoride or bifluorides may be used or mixtures of any of these may be employed.

The concentration of stannous chloride may vary from about thirty-seven and one-half to one hundred and fifty grams per liter and the alkali fluoride may similarly vary from thirty-seven and one-half to one hundred and fifty grams per liter. More specifically, it is desired to maintain the concentration of the stannous chloride and the alkali fluoride between about sixty and one hundred grams per liter.

More important, perhaps, than the mere concentration of stannous chloride and alkali fluoride is the molar ratio of these materials as related to the pH at which the bath is operated. An empirical formula which has been found satisfactory is as follows:

Mols SnCl where MB is an alkali fluoride and SnClz is stannous chloride.

The following conditions should be adhered to for successful use of the above formula:

(1) The constituents are used within the pH range of pH 1 to pH under conditions in which they are soluble in the plating bath, the tin content being maintained within the reasonable limits of 0.05 mol to 2 mols of tin metal per liter of solution. It may additionally be noted that generally it is desirable that the concentrations of stannous chloride and alkali fluoride be more than about grams per liter.

(2) The ratio of alkali fluoride to tin chloride for any given tin content is controlled by the value of It. It is then found that k is related to the pH of operation of the bath in such a way that for optimum operation at any given pH, is equals 0.55. However, it will be understood that in commercial operation good results may be obtained with values of k between the broad limits of Ic=0.l to lc=1.0. It is more particularly preferred to stay within the limits, lc=0.3 to k=0.7.

(3) The mol ratio of NIF $11012 should fall Within the limits of 2 and 12. It is preferred that the ratio equals 6 when k equals 0.55.

(4) The pH of the formula is the maximum at which the bath is stable while the optimum pH for plating is within the range from about 1 to 5 and preferably the pH should be in the range from about 2 to 4, A bath formulation that is stable at a given pH may also be stable at a lower pH but the preferred ranges are those within which addition agents are generally most effective.

In the practical application of the formula, since in ordinary use the pH of operation will be preselected, it will be fixed at the desired optimum value, and the amount of tin which it is necessary to have in the bath will be known, it may be best to express the equation in a form as shown below which may be used to calculate the amount of alkali fluoride compound required.

pH (Mols SnCl It As an example of the use of this formula let MF equal sodium fluoride and let it equal 0.55. The conditions selected are 0.33 mol of stannous chloride to be used at a pH of 4. Then to calculate the mols of sodium fluoride using the above equation:

(4) (0.33) 2.4 mols of sodium 0.55 fluoride required The acidity of the bath may be that which results from the bath constituents though adjustments of the pH may be made as desired. Generally, as mentioned above, the pH will fall within the range of about pH 1 to 5 while more specifically it is desired to have the pH from about 2 to 4.

In addition to observing the above conditions it will be found desirable so to adjust the bath composition as to lead to a static solution potential within a predetermined range. The solution potential, P, should not fall outside the limits of the following two equations:

In this formula, pH as indicated above, should have a value between 1 and 5 or, preferably, between 2 and 4.

After a solution has been prepared with constituents selected according to the methods given above in some detail, then the solution should be examined as to its potential. This can of course be done by making up a small amount of solution first and then adjusting the entire bath composition in accordance with the findings. If the solution potential is below the values given for P inthe above formulae, then it may be increased (made more negative) by increasing the MF/SnClz ratio; if the potential is too high it may be lowered by decreasing the MF/SnClz ratio. In adjusting the potential it will be noted that the potential increases (becomes more negative) with an increase in pH and decreases with a decrease in pH. Ordinarily potential will not be adjusted by changing the pH, though this means of adjustment is available if it is preferred to use some preselected ratio of MF to SnClz.

The potential may be determined in any suitable manner as by connecting a poteniometer across a piece of tin metal and a calomel half cell in customary manner. The static solution potential of tin against the bath is then obtained as volts after corrections are made for the calomel half cell.

The bath temperature is that customarily used for tin-plating baths, and deposits are obtained at room temperature. It is ordinarily preferred, however, to use the bath at a temperature from M ols sodium fl uoride about 55 to 65 C. in order to secure the optimum quality of deposit over a broad current density range.

BATH X Grams per liter Stannous chloride 75.0 Sodium fluoride 37.5 Sodium bifiuoride 37.5

Organic addition agents may advantageously be employed in any of the foregoing baths to improve the appearance and characteristics of tin deposits. One or more organic addition agents may be used and there may be included in the bath, for instance, sulfite cellulose waste or a naphthol sulfonic acid. Gelatin or glue may be used to advantage for some uses but it will be found that glue and certain other organic agents are not too satisfactory when the deposit is to be heat-fused or lacquer-baked.

Metal brighteners may also be included in any of the foregoing baths and there may be used small amounts of a soluble compound of the triad metals of the iron group including iron, cobalt, and nickel. There may, for instance, be used nickel chloride, nickel sulfate, or cobalt chloride, or cobalt sulfate, or iron chloride, or iron sulfate. The amount of the metal compound to use may readily be determined by a few simple tests and it will generally be found that from about 2 to 10 grams per liter is suitable. While iron exercises a beneficial effect on brightness, it promotes oxidation of stannous tin and is for this reason undesirable.

According to the present invention there is included in any tin electrodepositing bath, such as those shown above, a bath-soluble polydioxolane. The presence of such a polydioxolane profoundly modifies the character of deposit obtained from such a bath.

The polydioxolane may most conveniently be marketed in tin-plating compositions which contain some or all of the materials to be dissolved in water to make a tin-plating bath. Thus they may be sold in mixtures with tin compounds and any of the other bath components or additions as above described. Maintenance compositions may similarly be compounded with a polydioxolane and other materials required for bath maintenance.

As has been indicated the polydioxolanes should be bath-soluble. That is, they must be soluble enough to permit them to exercise an effect in the bath. They should be hydrophilic and even if they are very difficultly soluble they may be added to a plating solution in a solvent or dispersed in other manners already well known to the art.

While any bath-soluble polyether may advantageously be employed for the modification of tin deposits according to the present invention it is preferred to use compounds containing a multiplicity of aliphatic ether groups.

A polydioxolane may be a self-polymer, a copolymer with a reactive organic material, or a reaction product of a self-polymer with an organic material as further described below. Polydioxolanes may be represented by the formula:

(R200 s),.' 1 R1 1 I ]n" 4 In this formula R1 and R4 may be hydrogen, OH,

or a monovalent organic radical such as alkyl, alkoxy, aryl, aryloxy, aralkyl, alkaryl, acyl,

amine, amido, thialkyl, and thioaryl. R2 and R: are bivalent hydrocarbon radicals, preferably -CH2 or CH2CH2, and are difierent. R5 and Rs are, preferably, as just stated, hydrogen but they may be monovalent hydrocarbon radicals. In the expression, n, n, and n" are integers.

As typical of polydioxolanes suitable for the modification of tin deposits according to the present invention there may be mentioned recently developed products prepared by the copolymerization of 1,3-dioxolane with other materials such as organic acids, alcohols, ethers, esters, nitriles, and the like. The polydioxolanes produced, for instance, by reacting a monocarboxylic acid with 1,3-dioxo1ane have the generic formula:

2 R1CO(OCH2OCH2CH2)1OH or perhaps have the formula:

3 R (OCH2CH2OCH2) OH in which n is an integer and R1 is an alkyl, substituted alkyl, aryl, or substituted aryl group, such, for example, as methyl, ethyl, propyl, butyl, amyl, and the higher alkyl groups, such as dodecyl, stearyl, cetyl, ceryl, etc.; phenyl, tolyl, salicyl, etc.; the alkoxy alkyls, such as methoxy methyl, methoxy-menthoxy, methyl, ethoxy methyl, and so forth; hydroxy methylene, hydroxy ethylene, methyl hydroxy ethylene, etc.; and in fact any substitution in the R position. Similarly, if the interpolymerization is effected with a dicarboxylic acid the products probably have the formula:

l R1CO (OCI-IzOCHzCHz) OH where n is an integer and the R1 groups are similar to those designated above except that they are divalent. Similarly, polycarboxylic acids may be reacted to give corresponding products and as examples of polycarboxylic acids, including d1- carboxylic acids, there may be mentioned adipic, phthalic, terephthalic, aspartic, glutamic, oxalic, mesoxalic, tartaric, tartronic, succinic, citric, malic, maleic, camphoronic, tricarballylic, aconitic, fumaric, sebacic, glutaric, pimelic, suberic, azelaic, malonic, mellitic, and trimesic. If esters are reacted instead of acids an alkyl group will in many instances be substituted for the terminal hydrogen atoms in the above formula.

It is possible that the products described have either a linear or cyclic form or both and it will furthermore be understood that there is good theoretical foundation for the chemical structures shown but the description by formulas and by reactions is given for purposes of illustration and not by way of limitation,

The high molecular Weight products now being described as polydioxolanes include all products designated in the above formulas and the products resulting from the reactions given containing at least two 1,3-dioxolane groups and the products which they illustrate. In other words, the term will include among other things all products containing at least two 1,3-dioxolane residues, which residues have the structure 1) CH2OCH2CH2O-, (2) CI-I2OCH2CH2OH, or (3) CH2C'H2OCH2O'H, the residues (2) and (3) are at the end of the polymer chain, while (1) is Within the chain. The substituted 1,3-dioxolane residues will have a similar configuration with the exception that one or more of the hydrogens designated will be substituted.

Acids, their esters and dehydration products, alcohols, phenols, ketones, amides, and glycols may be reacted to form a polymer with 1,3-dioxolane which has the chemical formula with numbering as shown,

Ea UHz-O which cyclic glycol formal may be obtained by reacting iormaidehyde with ethylene glycol. Products with substitutions in the two position can be readily obtained by reaction of ketones or other aldehydes either aliphatic or aromatic with ethylene glycol. Thus, by way of example, many compounds are obtained which may be employed in accord with the invention, such as 2-methyl-l,3diox0lane, 2-ethyl-l,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2,2-diethyl-1,3-diox olane, 2phenyl-l,3-dioxolane, 2,2-methyl-phenyl-l,3-dioxolane, and higher dioxolanes substituted in like manner which may, for example, be obtained from ethylene glycol and acetaldehyde, propanol, acetone, diethyl ketone, benzaldehyde, methyl phenyl ketone, and higher substituted aldehydes respectively. The invention likewise contemplates the use of 1,3-diX0lanes substituted in the 4 and/or 5 positions. dioxolanes are obtained by the interaction of substituted 1,2-glycols with aldehydes, for example, 1,3-propylene glycol formaldehyde will give 4-methyl-1,3-dioxolane and similarly the following dioxolanes can be readily prepared from formaldehyde and the corresponding glycols: 4-ethyl-l,3-dioxolane, 4-propy1-1,3-dioxolane, 4,5-dimethyl-l,3-dioxolane, and the like.

Dioxolane can be combined with, for instance: (1) monocarboxylic aliphatic acids, such, for example, as: formic, acetic, propionic, nand iso-butyric, nand iso-valeric acid, trimethyl acetic and the higher acids of this class such, for example, as: hydroxyacetic, hydroxypropionic, lactic acids and their dehydration products such as glycolid, glycolic anhydride, diglycolic anhydride, lactic etc.; the alkoxy substituted acids of the class such, for example, as: methoxy-, ethoxy-, propoxy-, methoxymethoxy-, ethoxymethoxy-acetic, propionic and higher like substituted acids; and the unsaturated acids such, for example, as: acrylic, alpha-substituted acrylic, (e. g. methacrylic), butenic, angelic, tiglic, oleic, ricinoleic, elaidic, erucic acids, etc.; (2) the monocarboxylic aromatic acids, such, for example, as: benzoic, phenyl-acetic, o-, m-, and p-tolyic, hydrocinnamic, o-, m-, p-totyl acetic, 0-, m-, and p-ethyl benzoic and mesitylenic acids; the substituted acids of the class such, for example, as: salicyclic, meta and para hydroxybenzoic, mandelic, tropic, oxybenzoic, and anisic acids and the unsaturated acids such, for example, as: cinnamic, atropic, phenyl-propiolic, and coumaric acids; (3) the carboxylic aliphatic acids such, for example, as: oxalic, malonic, succinic, glutaric, adipic, pimelic, camphoric acids, etc.; the hydroxy substituted acids of the class such, for example, as: tartronic, malic, tartaric racemic and other acids of this class such, for example, as: maleic, fumaric, trihydroxyglutaric, saccharic, mucic, isosaccharic, mesoxalic, oxalacetic. acetone dicarboxylic, dihydroxy-tartaric, and diaceto-succinic, tric arballylic, and citric acids; (4) the polycarboxylic aromatic acids such, for example, as: o-, m-, p-phthalic, hydro- These 1,3-

l I actant.

phthalic, 2,5-dihydroxy-terephthalic, and m'ellitic acids; and (5) such acids as: the ketone acids; pyruvic, phthalonic, levulinic, the acyl substituted acids, hydroxy-acetoxy, acetic, propionic, butyric, cyanacetic, sulianilic, tannic and thioacetic acids. The esters and polymers may also be made from the esters and dehydration products of the above acids, such as the anhydrides, polyacids, etc. Saturated and unsaturated fatty acid oils may likewise be reacted with the dioxolanes and, by way of example, there are included: cotton seed, rape, sesame, beechnut, linseed, poppy, sun flower, palm nut, coconut, Tall, soybean, china wood, corn, castor, and oiticica oils, as well as the triglycerides, tripalmitics, tristearics, etc. For convenience this reactant will hereinafter be referred to as the acidic reactant. In addition to the foregoing, dioxolane can be combined with (6) alcohols such as methyl, ethyl, propyl, lauryl, dodecyl, and methoxycthyl, with (7) phenols such as phenol, cresols, and alpha and beta naphthols, or with still other reactants such as polyvinvyl alcohol, polyethylene glycols, and olefinedienes.

Polydioxolanes suitable for the modification of tin deposits can be prepared by the interaction of dioxolane with the acidic reactant or other reactants. It is not necessary that there be pres ent equimolecular proportions of the dioxolane and the acidic or other reactant for it has been found that valuable products are obtainable when small amounts of the 1,3-dioxolane or its derivatives are used, say down to as low as one part thereof per 99 parts of the acidic or other re- The influence of the dioxolane on the resulting product, of course, will not be as great when it is used in low concentrations. Dioxolane may likewise be in excess to give a marked change in the properties of the resultin product. For example, the water-insoluble acidic reactants and generally those organic acids and esters having more than eight carbon atoms can be converted to water-soluble products if a sufiicient number of dioxolane groups are added. By varying the amount of dioxolane reacted, products can be obtained ranging from water-solubility to complete miscibility in water. Dehydration products of the acid, such as the polymeric acids; e. g. glycolids and lactics, etc., can be reacted in accord with this procedure to obtain products with valuable solubility characteristics.

The reaction can be effected at the temperatures ranging between and 300 C. and preferably between 0 and C. Atmospheric, subor superatmospheric pressures may be used, and if the last, pressures may range between 1 and 1000 atmospheres or higher. Normally excellent results are obtained at or about atmospheric pressure. If desired, the temperature of the reaction, especially when carried out at the boiling point of the reaction mixture, may be controlled by varying the pressure on the boiling reactants.

It has been found advantageous to carry out the reaction in the presence of an acidic type catalyst, such, for example, as sulfuric acid, phosphoric acid; the halogen acids, such as hydrochloric acid, hydrofluoric acid (alone or with BFs); boron fluoride (including its complexes with water, acids, esters, alcohols, and the like), paratoluene sulfonic acid, camphor sulfonic acid, and other acid catalysts of this general nature. Friedel-Crafts type catalysts other than BFB may be used, such as A1013, AlBla, FeCla, and so forth, as well as inorganic acids generally and their acid salts such as sodium acid sulfate, sodium acid phosphate. and so forth.

Instead of polymerizing dioxolane in the presence of reactants such as an organic acid, the dioxolane or substituted dioxolane may first be polymerized to yield a polydioxolane which is a self-polymer. The resulting polyglycolformals may be used as such for the modification of tin deposits according to the present invention or these may be substituted with any of the substituent groups mentioned in the foregoing. For instance, one may thus use the reactants just referred to after polymerization instead of using them in the polymerization.

The invention is further illustrated by the following examples:

Example 1 Grams per liter Stannous sulfate (SnSO l) 54 Sulfuric acid 100 "Polydioxolane 2,000 1.0

The white waxy-solid obtained by polymerizing 1,3-dioxo1ane to obtain a substance whose average molecular weight is approximately 1500, was added to a bath prepared as described under bath I. The material was completely soluble in the bath and was eifective in producing deposits that were smooth, adherent and sponge-free over a plating range of from to 100 amps/sq. ft,

The material was further used in such baths as III, V, VI, VIII, IX, and X and was found to be effective in producing good quality deposits from all baths in which it was tested, the deposits obtained being smooth, free of sponge and adherent over a wide current density range. Particularly good deposits were obtained from bath X in which 0.2'gram per liter of Polydioxolane 2000 was effective in preventing sponge formation and produced smooth lustrous adherent deposits over a current density range of from 3 to 120 amps/sq. ft.

Example 2 Another polymer of 1,3-dioxolane having an average molecular weight of 10.000 was similarly used in such baths as II, IV, VIII, and X. This material was likewise a white waxy solid. It was less soluble than Polydioxolane 2000 but was readily soluble in the plating baths in the form of an aqueous solution. From 0.1 to 3.0 grams per liter was effective in preventing the formation of sponge deposits and produced smooth, white, adherent. deposits over a wide current density range. Particularly good deposits were obtained by the presence of 0.8 gram per liter in bath IV from which smooth, lustrous, adherent deposits were obtained over the entire area of a I-Iull cell plate.

Example 3 The white waxy solid obtained by reacting ethylene glycol with 1,3-dioxolane and having an average molecular weight of 5,000 was used in baths I, V, VIII, and IX. It was readily soluble in water and in the plating baths and was effective in producing smooth, white, adherent deposits when present to the extent of from 0.1 to 5.0 grams per liter.

Example 4 The dark red gummy solid obtained by reacting 1,3-dioxolane with phenol was added in the form of its aqueous solution to baths I, V, VIII, IX, and X to the extent of from 0.1 gram per liter to 3.0 grams per liter and was found to be effective in producing deposits that were smooth, adherent and free of sponge. The deposits obtained from bath X were particularly beneficially affected by its presence, being smooth, lustrous, and adherent over a current density range of from 3 to 120 amps/sq. ft.

Example 5 The white pasty solid obtained by reacting 1,3- dioxolane with lauryl alcohol was used in baths II, III, VI, IX, and X and was found to be effective in concentrations of from 0.1 to 4.0 grams per liter. Smooth, white, adherent deposits relatively free from sponge or crystalline growths were obtained from baths II, III, VI, and IX, the deposits obtained from bath X being smooth and lustrous over the entire area of a Hull cell plate. The addition of this material caused the respective plating baths to become turbid in appearance and caused considerable foam to form during electrolysis.

Example 6 The white waxy solid obtained by reacting 1,3- dioxolane with stearic acid was used in baths I, IV, VII, IX, and X. Smooth, uniform, deposits that were free from sponge or crystalline growths were obtained when the material was present to the extent of from 0.1 to 3.0 grams per liter. Its effect upon the deposits and its appearance in the respective plating baths was very similar to that of lauryl alcohol glycolpolyformal described under Example 5.

Example 7 The water white liquid obtained by reacting 1,3- dioxolane with adipic acid was used in baths II, V, VII, IX, and X. From 0.1 to 5.0 grams per liter of the material allowed the deposition of smooth, white, adherent deposits of tin and was particularly effective in baths V, IX, and X. The material Was soluble in all proportions and allowed the respective baths to remain clear and colorless.

Example 8 The water white liquid obtained by reacting 1,3-dioxolane with methyl alcohol was used in baths III, VII, and IX. The deposits obtained by using from 0.1 to 5.0 grams per liter were similar to those of the above examples, being smooth, white, and adherent over a wide current density range. The material was soluble in all propor tions and allowed the solutions to remain clear and colorless.

Example 9 The light yellow colored liquid obtained by reacting 1,3-dioxolane with isobutanol n-propanol was used in baths II, VIII, and IX. It was very similar to the materials described in Examples 7 and 8 in both its effect upon deposits and physical characteristics.

Example 10 The clear colorless liquid obtained by reacting 1,3-dioxolane with acetone was used in baths HI, VI, and X. Its effect was somewhat les than that of the materials previously described, allowing the formation of sponge deposits at high current densities. Sponging at low current densities, however, was efiectively prevented by the presence of from 0.2 to 5.0 grams per liter, the deposits being smooth and adherent up to 60 amperes per square foot in baths III and VI and were smooth and lustrous up to amps/sq. ft. in bath X. The

material was soluble in all proportions, allowing the baths to remain clear and colorless.

Ezcample 11 The clear colorless liquid obtained by reactin 1,3-dioxolane with methoxy ethanol (the monomethyl ether of ethylene glycol), was used in baths IV, VIII, and X. The deposits obtained in the presence of from 0.1 to 4.0 grams per liter of this material were somewhat improved over those of the previous example, particularly in bath X which produced uniform lustrous deposits up to 80 amperes per square foot. The material was soluble in all proportions and allowed the respective baths to remain clear and colorless.

Example 12 The honey colored liquid obtained by reacting 1,3-dioxolane with methyl glucoside was used in baths I, VI, and IX. The deposits obtained in the presence of from 0.1 to 5.0 grams per liter of this material were smooth, and adherent up to 80 amps/sq. ft. The material was soluble in all proportions and allowed the respective baths to remain clear and colorless.

Example 13 The solid white product obtained by reacting dioxolane with vinyl acetate forms a substance Whose formula is unknown but contains the polydioxolane type of structure (CH2CH2OCH2O) in the main chain of atoms. Smooth, white, adherent deposits up to 120 amps/sq. it. were obtained from baths VIII and X in which this material was used. Its presence caused a slight cloudiness in the baths, indicating that the material was only partially soluble.

Polydioxolanes may be used in tin-plating baths in minor amounts as shown above. The amount of a polydioxolane to use can most easily be determined in any particular instance by trying out various amounts in the specific plating bath and in the specific type of use by routine methods already well-known to the practical plater. It may be indicated that in general from about 0.001 to grams per liter of a polydioxolane will be found suitable. Too small an amount may not be sufliciently efiective and too much is wasteful, and, if greatly excessive, may interfere with bath operations.

We claim:

1. In a process for the electrodeposition of tin the step comprising efiecting electrodeposition from an aqueous, tin-plating bath which contains a soluble tin compound, the process comprising effecting electrodeposition in the presence of 0.001 to 25 grams per liter of a bathsoluble compound containing at least two 1,3- dioxalane groups.

2. In a process for the electrodeposition of tin the step comprising effecting electrodeposition from an aqueous, tin-plating bathwhich contains a soluble tin compound, the process comprising effecting electrodeposition in the presence of 0.001 to 25 grams per liter of a. bathsoluble polymer of 1,3-dioxalane terminally substituted with an alkyl radical.

3. In a process for the electrodeposition of tin the step comprising effecting electrodeposition from an aqueous, tin-plating bath which contains a soluble compound, the process comprising efiecting electrodeposition in the presence of 0.001 to 25 grams per liter of a bath-soluble polymer of 1,3-dioxalane terminally substituted with an aryl group.

4. In a process for the electrodeposition of tin the step comprising effecting electrodeposition from an aqueous, tin-plating bath which contains a soluble tin compound, the process comprising effecting electrodeposition in the presence of 0.001 to 25 grams per liter of a bathsoluble self-polymer of 1.3 dioxalane.

5. In a process for the electrodeposition of tin the step comprising efiecting electrodeposition from an aqueous bath which contains an alkali fluoride, stannous chloride, and 0.001 to 25 grams per liter of a bath-soluble compound containing at least two 1,3-dioxalane groups, the composition having a stannous chloride concentration of between about 37.5 and grams per liter and the bath satisfying the equation:

k(Mols MF) pH Mols SnCl wherein the following conditions are simultaneously true; pH is equal to about 1 to 5, It has a value from 0.1 to 1.0, MB is alkali fluoride, and the mol ratio is about from 2 to 12, the static solution potential of tin in the bath being equal in volts to from 0.055 pH -0.265 to 6. In a process for the electrodeposition of tin the step comprising efiecting electrodeposition from an aqueous bath which contains an alkali fiuoride, stannous chloride, and 0.001 to 25 grams per liter of a bath-soluble polymer of 1,3-dioxalane terminally substituted with an alkyl radical, the composition having a stannous chloride concentration of between about 37.5 and 150 grams per liter and the bath satisfying the equation:

k(Mols MF) wherein the following conditions are simultaneously true; pH is equal to about 1 to 5, It has a value from 0.1 to 1.0, MP is alkali fluoride, and the mol ratio is about from 2 to 12, the static solution potential of tin in the bath being equal in volts to from -0.055 pH 0.265 to k(Mols MF) Mols SnCl wherein the following conditions are simultaneously true; pH is equal to about 1 to 5, It has a value from 0.1 to 1.0, MB is alkali fluoride, and the mol ratio 13 is about from 2 to 12, the static solution potential of tin in the bath being equal in volts to from -0.055 pH 0.265 to 8. In a process for the electrodeposition of tin the step comprising effecting electrodeposition from an aqueous bath which contains an alkali fluoride, stannous chloride, and 0.001 to 25 grams per liter of a bath-soluble self-polymer of 1,3- dioxalane, the composition having a stannous chloride concentration of between about 37.5 and 150 grams per liter and the bath satisfying the equation:

k(Mols MF) Mols SnOl wherein the following conditions are simultaneously true; pH is equal to about 1 to 5, 7c has a value from 0.1 to 1.0, MP is alkali fluoride, and the mol ratio MF S1101;

is about from 2 to 12, the static solution potential of tin in the bath being equal in volts to from -0.055 pH 0.265 to 9. A tin electrodepositing composition comprising an alkali fluoride, stannous chloride, and 0.001 to 25 grams per liter of a bath-soluble compound containing at least two 1,3-dioxalane groups, the composition upon being dissolved in water being adapted to give a stannous chloride concentration of between about 37.5 and 150 grams per liter and satisfying the equation:

wherein the following conditions are simultaneously true; the pH is equal to about 1 to 5, It has a value from 0.1 to 1.0, MF is alkali fluoride, and the mol ratio SnCl is about from 2 to 12, the static solution potential of tin in the bath being equal in volts to from --0.055 pH 0.265 to wherein the following conditions are simultaneously true; the pH is equal to about 1 to 5, is has a value from 0.1 to 1.0, MF is alkali fluoride, and the mol ratio MF Such is about from 2 to 12, the static solution potential of tin in the bath being equal in volts to from .14 0.055 pH-0.265 to 12. A tin electrodepositing bath comprising an aqueous solution of an alkali fluoride, stannous chloride, and 0.001 to 25 grams per liter of a bath-soluble polymer of 1,3-dioXalane terminally substituted with an aryl group, the stannous chloride concentration being between about 37.5 and grams per liter and the bath satisfying the equation:

k(Mols MF) Mols SnCl wherein the following conditions are simultaneously true; the pH is equal to about 1 to 5, is has a value from 0.1 to 1.0, MP is alkali solution potential of tin in the bath being equal in volts to from -0.055 pH 0.265 to 13. A tin electrodepositing bath comprising an aqueous solution of an alkali fluoride, stannous chloride, and 0.001 to 25 grams per liter of a bath-soluble self-polymer of 1,3-dioxalane, the stannous chloride concentration being between about 37.5 and 150 grams per liter and the bath satisfying the equation:

wherein the following conditions are simultaneously true; the pH is equal to about 1 to 5, It has a value from 0.1 to 1.0, MP is alkali fluoride, and the mol ratio is about from 2 to 12, the static solution potential of tin in the bath being equal in volts to from 0.055 pH 0.265 to ALLEN G. GRAY. WILLIAM FRANKLIN GRESHAM. DONALD JOHN LODER.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Name Date Brown Oct, 25, 1938 Barrett et al Aug. 13, 1940 Steindorff et al Sept. 3, 1940 Nachtman Dec. 16, 1941 Schlotter Jan. 27, 1942 Johnson Mar. 3, 1942 Loder et al. Jan. 5, 1945 Nachtman Mar. 6, 1945 Beaver Dec. 18, 1945 Schweikher Sept. 10, 1946 FOREIGN PATENTS Country Date Great Britain Apr. 16, 1931 Great Britain July 22, 1935 Great Eritain Feb. 27, 1936 OTHER REFERENCES Industrial and Engineering Chemistry, Jan. 1941, pages 16-22.

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